For the past two decades, camcorders, or video camera-recorders, have been a familiar sight throughout the world. They have been particularly in demand in the United States, Japan, Europe, and many other countries because they are inexpensive while extremely useful for numerous purposes. Camcorders and digital still cameras both take pictures using image sensors such as charge-coupled devices (CCD) or CMOS devices. To create a video signal, a camcorder image device must take many pictures every second, which the camera then combines to give the impression of movement. Analog camcorders contain two basic parts: (1) a camera section, consisting of an image sensor, lens and motors to handle the zoom, focus and aperture; and (2) a VCR section, which is a typical but small TV VCR. The function of the camera components is to receive visual information and transform it to electronic video signals.
Digital camcorders have the same elements, but have an additional component that takes the analog information the camera gathers and transforms it to digital data. Digital camcorders are so popular because their recorded information is not as prone to degradation, such as fading, as that of analog cameras. Video information in digital form can also be loaded onto computers, and easily edited, copied, and e-mailed.
The lens in a camcorder serves to focus light onto a small semiconductor image sensor. This sensor, such as a CCD, measures light with a small array of many tiny light-sensitive diodes, called photosites or pixels. Each photosite measures the amount of light that illuminates a particular point, and transforms this information into electrical charges. A brighter image is represented by a higher electrical charge, and a darker image is represented by a lower charge. An image sensor then creates a video picture by recording these light intensities.
Similarly, to create a color image, a camcorder has to detect the levels of each color of light. Since a full spectrum of colors can be created by combining the three colors red, green and blue, a camcorder only needs to measure the levels of these three colors to be able to reproduce full-color pictures. Some high-end camcorders use three separate chips to measure the intensity of these three basic colors while other less expensive camcorders get by with only one image sensor by fitting permanent color filters to individual photosites.
Camcorders in different parts of the world are designed in conformity with the local standards of pixel resolution, number of frames per second (fps), etc. The three most commonly used standards are NTSC, PAL, and SECAM. NTSC standard is used in North and South America, Japan, and 30 other countries. This standard requires 30-fps, 720×480 rectangular pixel resolution, and 575 scan lines. PAL format is used in Europe, Africa, the Middle East, Australia, China, and others and requires 25-fps, 720×576 rectangular pixel resolution, and 625 scan lines. Finally, SECAM format is used in France, the former Soviet Union countries, and others. It also requires 25-fps, 720×576 rectangular pixel resolution, and 625 scan lines.
It is important to note that in those countries in which a 50-Hz AC power system is used, the fps is 25 and in those with 60-Hz, the fps is 30. One main reason is the simplicity of design when the required number of aperture closures is an integer multiple or a factor of the power supply frequency. As a side benefit, it will synchronize the aperture closures with the surrounding pulsating lights, such as fluorescent lights. This synchronization makes the aperture opening coincide with the same light intensity of the pulsating light as in the previous openings.
On the other hand, if the aperture closures and the pulsating of the light are out of phase, the light intensity will vary at each aperture opening and will cause “flickering.” This is the case when U.S.-made camcorders operate in Japan under fluorescent lights, or vice versa. There is a need for a camcorder that can automatically detect the frequency of the surrounding pulsating lights and can adjust its frame rate accordingly.